Touch sensors are used on an ever-increasing number of devices. Users enjoy the tactile feel, or haptic sensation, of tapping a surface to launch a program or to select an item from a menu. These haptic sensations also add to the users' sensations and enjoyment when playing computer games.
As one example, touch sensors such as pressure-sensitive discs are used on MP3 digital audio players. A user traces a path along a contact surface of the displacement measuring disc to scroll through menus containing play lists and the like.
These touch sensors have several drawbacks. First, the signals they generate can vary depending on the force that a user applies when contacting the touch sensor. These signals are often dependent on a resistance of a portion of the touch sensor contacted, and this resistance can vary non-uniformly when large forces are exerted on a surface of the touch sensor, such as when a user gets emotionally involved playing a computer game. These forces, when translated into signals used by the computer game, can generate counterintuitive position values.
In addition to the force that a user contacts a touch sensor, the speed with which he contacts the touch sensor can non-uniformly affect the signals generated by the touch sensor.
Some prior art systems, such as force feedback devices, typically provide hard stops to limit the motion of a device such as a joy stick within a constrained range. Sensing the position of the joy stick is exacerbated at the hard stops. For example, when the user moves the joy stick fast against the hard stop, the compliance in the system may allow further motion past the hard stop to be sensed by the sensor due to compliance and inertia. However, when the joy stick is moved slowly, the inertia is not as strong, and the sensor may not read as much extra motion past the hard stop. These two situations can cause problems in sensing an accurate position consistently.
The inconsistent position reporting problem is further exacerbated with variable device joysticks and pointing devices being incorporated into cell phones and personal digital assistants (PDAs) imposing additional restrictions on the height and size of such devices requiring a miniature form factor or elevation.